The accurate reproduction of patterns on the surface of a semiconductor substrate is critical to the proper fabrication of semiconductor devices. The semiconductor substrate may have undergone previous fabrication processes and may already feature layers and structures created by those fabrication processes. Improperly reproduced patterns can result in semiconductor devices that do not operate to design specifications or do not operate at all. For example, transistors can be created with improperly sized gates, conductors can be created that are short circuited or open circuited with other conductors or devices, structures can be created with wrong geometries, and so forth. Improperly reproduced patterns can reduce the yield of the fabrication process, thereby increasing the overall cost of the product. The reproduction process typically involves the use of optical lithography to reproduce the patterns onto the surface of the semiconductor substrate that is subsequently followed with a variety of processes to either subtract (for example, etch) and add (for example, deposit) materials from and to the semiconductor substrate.
However, as the dimensions of the structures making up the patterns continue to become smaller, their sizes approach (in some cases, the dimensions of the structures are smaller than) the wavelength of the light used in optical lithography, the interference and processing effects can cause distortions and deviations in the patterns as they are reproduced onto the semiconductor substrate. Such distortion becomes quite complex in current lithographic systems where the structures being imaged are much smaller than the wavelength of the light used (e.g., 20 nm structures may be patterned using 193 nm wavelength). In addition to the relationship between structures of the patterns and the wavelengths of the light, other factors that can cause distortion include the numerical aperture of the imaging system, the minimum pitch between structures in the pattern, and normal levels of photolithography process variation. The result being a reproduced pattern having a dramatically different appearance from the pattern being reproduced, also known as the intended pattern. The distortions and deviations in the reproduced pattern are dependent upon the characteristics of the pattern, such as the shape and size of the structures in the pattern, the presence of neighboring patterns and structures around the pattern, as well as the process conditions. For example, the interactions of the light with the structures making up a pattern can result in the reproduced pattern having rounded corners, bulges towards another elements, and so forth.
Hence, methods for correcting these and other unwanted effects are required.